1. Field of the Invention
The present invention relates to a semiconductor laser device and particularly to a semiconductor laser device that can suppress increase in electric current during driving thereof in a long term.
2. Description of the Background Art
A semiconductor laser device is utilized as a light source for reading and/or writing signals from and/or on an optical storage medium such as a compact disk (CD), a digital versatile disk (DVD), or a blue ray disk. For reliability required of the semiconductor laser device, consideration is given to the device's lifetime that is determined from increase in driving-current of the device on condition of a constant optical output.
A bluish violet semiconductor laser device made of nitride and placed on the market in recent years has a shorter lifetime as compared to a conventional semiconductor laser device for emitting infrared or red light for the CD or the DVD and thus it is necessary to extend its lifetime in the future. Furthermore, it is also desirable that the semiconductor laser device for emitting infrared or red light is further improved in its lifetime with increase in its output.
In order to improve the lifetime of the semiconductor laser device, it is generally necessary to reduce crystal defects in the semiconductor, and in the past, the device's lifetime has been improved with advance of crystal growth technology (refer to Japanese Patent Laying-Open No. 2002-237659, for example).
However, the advance of crystal growth technology is saturating, and improvement of the device's lifetime by reduction of the crystal defects is now no longer expected.